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Understanding 4 wheel drive to repair my truck

Discussion in 'Chevy Suburban Forum (GMC Yukon XL)' started by wdc1, Jan 19, 2014.

  1. wdc1

    wdc1 New Member

    2003 LS Suburban flex 5.3 4x4 abs

    In drive 2wd the rear drive shaft spins. I know this is right.

    In 2wd the front drive shaft also spins? Mine does

    The transfer case control motor tells the front differential to go into 4 wheel drive when you push the 4WH?

    The front wheel drive actuator then tells the right and left drive shafts to connect to the transfer case and wheels and then 4 wheel drive occurs?

    My truck goes to two and 4 wheel easy with no issues and truck drives fine but right and left front two axles are spinning while in two or 4.

    I know I am in 2 or 4 by hitting gas a little on big snow patch and feeling what tires spin.

    No error codes. Shift buttons perform correctly. No noises

    Any help appreciated on educating me so I may purchase the correct part.
  2. RayVoy

    RayVoy Active Member 1000 Posts

    The front and the rear axle assemblies use a differential that is considered "open" (even if the rear uses a G80 locker diff, the diff normally operates in the open position).

    Place the truck on 4 jack stands, engine off, transmission in neutral, transfer case in 2wd.

    Turn one rear wheel by hand, the other wheel may not turn, or it may turn backwards (both are normal) The rear driveshaft may turn, or may not turn.

    Have someone hold one rear wheel while you turn the other rear wheel. The rear driveshaft will turn.

    Go to the front. The passenger side front axle has an electro-mechanical disconnect that should have the passenger wheel disconnected from the front differential. If you turn this wheel, nothing else should turn.

    If you turn the front driver's side wheel, the passenger side front wheel should not turn, the front driveshaft may, or may not turn.

    When the t-case is shifted to 4WD, the following is the sequence, operating the 4wd switch will have the Transfer Case Control Module (TCCM) command the shift motor (in the t-case) to move to the appropriate position (but not to operate the front clutches). The encoder, on the shift motor reports the movement to the TCCM, the TCCM then commands the motor in the front passenger axle disconnect to operate and to engage the axle halves. When engaged, a signal is sent to the TCCM indicating the engagement. The TCCM then commands the encoder/shift motor to operate the clutches in the t-case to send power forward. Locking the front driveshaft to the rear driveshaft.
  3. Jamm3r

    Jamm3r New Member

    It will usually turn a little because of friction

    With the vehicle parked and in 2wd you can reach up and try to turn it by hand. It should turn freely. If it does not then either the transfer case is stuck in 4wd or the axle disconnect isn't disconnecting.
  4. wdc1

    wdc1 New Member

    I have noticed I hear a noise when it goes from 4 hi to 2wd but not back or a noise when I go auto 4wd to 2wd but not back and sometimes if I switch back and forth while at idle a few times the button stops switching. Later on it works fine. I have heard these buttons are defective and once in a while I have service 4 wd and it goes away,

    - - - Updated - - -

    As a follow up I did a few things. I think it was difficult to hear the truck switching to different drives. Went to quiet garage. Go 2WD TO 4WD and reverse hear motor noises when button pushed, go 2wd to auto and back hear motor noises when button pushed go from 4wd to auto and reverse hear motor noises when button pushed. Is this the actuator or the transfer case module? I also did something I never did before in the trucks life, switched back and forth between 4lo and 4hi. Followed manual since I know if done incorrectly very serious damage can occur. Heard the normal clunk per manual. Was thinking maybe since I never used it may resolve the situation. Also was able to easily spin front drive shaft. Will check if it is spinning at the same speed as drive shaft like before when I have it on jack stands. Thanks for all your help. Will keep you posted and I have learned a lot from you guys. I have virtually no one in my neck of the woods who works on cars, trucks. They just bring it in to the stealer ship or regular stealer shop. What happened to the good old days? It helps me to think out of the box when I have people like you.
  5. RayVoy

    RayVoy Active Member 1000 Posts

    The motor noise is the shift motor (also called the encoder motor) that is in the transfer case.


    And, AFAIK, shifting back and forth from 4HI to 4LO won't cause any problems. If you do it correctly, it shifts; if you do it incorrectly, it does not shift and lights on switch will flash. It has a built in safe guard against mistakes.
  6. wdc1

    wdc1 New Member

    Thank You for your help. By the way the front shaft does spin some while the back shaft spins but at a much faster rate so appears it is fine.

    - - - Updated - - -

    By the way will have the car on four jack stands soon. I have two new 3 ton hein warners and 2 old 3 ton sears jacks and do not fell safe putting these sears jacks under even on the lighter back end. Just looking at the difference in build tells me that. Ok for car. New hein warners are coming in soon.
  7. wdc1

    wdc1 New Member

    Results for Rayvoy



    Place the truck on 4 jack stands, engine off, transmission in neutral, transfer case in 2wd. All 4 wheels off ground,neutral, 2wd
    Turn one rear wheel by hand, the other wheel may not turn not turn, or it may turn backwards (both are normal)(backwards) The rear driveshaft may turn, or may not turn. Turns on front spin not reverse

    Have someone hold one rear wheel while you turn the other rear wheel. The rear driveshaft will turn. Yes

    Go to the front. The passenger side front axle has an electro-mechanical disconnect that should have the passenger wheel disconnected from the front differential. If you turn this wheel, nothing else should turn. Yes wheel and half shaft

    If you turn the front driver's side wheel, the passenger side front wheel should not turn, the front driveshaft may, or may not turn. Only drivers side wheel turns and half shaft

    Note :
    1. Checked transmission fluid, full on hot line. Checked per manual instructions since its tricky to check,(red, not discolored).
    2. I hear a loud sound from front of engine that had gotten louder over time like a drag on the engine as I go faster.
    3. I know the water pump is going , leaking a little. 125,000. I heard a clunk a while ago. Maybe this is the sound.
    4. If I listen inside the car I can hear something that sounds like bearing rumbling but very very subtle.
    4. The shifting from 2 to 4wd to auto 4wd and 4wd to 4 wdlo work fine. The car is off so I clearly hear the shift or encoder motor.


    - - - Updated - - -

    Just to add another thing in drive, 2wd, the front half axles do not turn but the front drive shaft does but not as fast as the rear drive shaft. The front drive shaft can be moved by hand while in park.
  8. wdc1

    wdc1 New Member

    Just removed water pump and it was leaking and found out my power steering pump pulley is very loose. Replacing.
  9. wdc1

    wdc1 New Member

    I think I know what it is, the bearings. Replaced right ones at 100 and left one has some play definitely.

    Front end is tight.
  10. wdc1

    wdc1 New Member

    Took bearings out which are apart of the hub. They were toast. Grinding on spinning.

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